Cloud Radar Observations of Diurnal and Seasonal Cloudiness over Reunion Island

Atmosphere

François Bonnardot¹  Julien Delanoë²  Edouard Lees³  Jonathan Durand³  Olivier Bousquet³ 

[1] Direction Interrégionale de Météo-France pour l’Océan Indien, Saint-Denis, 97490 Sainte-Clotilde, France;Laboratoire Atmosphère, Milieux et Observations Spatiales (UMR 8190 LATMOS), CNRS/Sorbonne Université/USVQ, 78280 Guyancourt, France;Laboratoire de l’Atmosphère et des Cyclones (UMR8105 LACy), Université de La Réunion, CNRS, Météo-France, 97400 Saint-Denis, France;

关键词: cloud radar;    BASTA;    Indian Ocean Subtropical Dipole;    Reunion Island;    integrated water vapor;    Southwest Indian Ocean;   

DOI  :  10.3390/atmos12070868

来源: DOAJ

【 摘 要 】

In November 2016, a 95 GHz cloud radar was permanently deployed in Reunion Island to investigate the vertical distribution of tropical clouds and monitor the temporal variability of cloudiness in the frame of the pan-European research infrastructure Aerosol, Clouds and Trace gases Research InfraStructure (ACTRIS). In the present study, reflectivity observations collected during the two first years of operation (2016–2018) of this vertically pointing cloud radar are relied upon to investigate the diurnal and seasonal cycle of cloudiness in the northern part of this island. During the wet season (December–March), cloudiness is particularly pronounced between 1–3 km above sea level (with a frequency of cloud occurrence of 45% between 12:00–19:00 LST) and 8–12 km (with a frequency of cloud occurrence of 15% between 14:00–19:00 LST). During the dry season (June–September), this bimodal vertical mode is no longer observed and the vertical cloud extension is essentially limited to a height of 3 km due to both the drop-in humidity resulting from the northward migration of the ITCZ and the capping effect of the trade winds inversion. The frequency of cloud occurrence is at its maximum between 13:00–18:00 LST, with a probability of 35% at 15 LST near an altitude of 2 km. The analysis of global navigation satellite system (GNSS)-derived weather data also shows that the diurnal cycle of low- (1–3 km) and mid-to-high level (5–10 km) clouds is strongly correlated with the diurnal evolution of tropospheric humidity, suggesting that additional moisture is advected towards the island by the sea breeze regime. The detailed analysis of cloudiness observations collected during the four seasons sampled in 2017 and 2018 also shows substantial differences between the two years, possibly associated with a strong positive Indian Ocean Southern Dipole (IOSD) event extending throughout the year 2017.

【 授权许可】

Unknown